The disclosures of the following priority applications are herein incorporated by reference:
Japanese Patent Application No. 2000-018546 filed Jan. 27, 2000
Japanese Patent Application No. 2000-154187 filed May 25, 2000
1. Field of the Invention
The present invention relates to a focal point detection apparatus having a focal point detection area over a wide range within the photographic field and a camera that employs the focal point detection apparatus.
2. Description of the Related Art
Focal point detection apparatuses employed in single lens reflex cameras in the known art often adopt the following focal point detection method. This type of focal point detection apparatus guides two subject images manifesting a parallax to a couple of rows of. photoelectric conversion elements and judges the focal adjustment state by calculating the degree of the relative offset manifesting between the two images in correspondence to the image outputs from the individual photoelectric conversion element rows.
Japanese Laid-Open Patent Publication No. H9-184966 discloses a focal point detection apparatus that enables a focal point detection over a wide range within the photographic field by adopting the phase difference detection method described above. In this focal point detection apparatus, a two-dimensional image sensor is utilized in place of the pair of photoelectric conversion element rows, in order to assure a wide range of focal point detection area around the optical axis. In addition, in order to expand the focal point detection area in the photographic field along the vertical direction, i.e., the direction along which the short side of the image plane extends, a concave mirror is employed to constitute a sub-mirror that guides the light flux for focal point detection having been transmitted through the main mirror to the focal point detection apparatus.
By utilizing the concave mirror, the focal point detection apparatus in the prior art described above can be manufactured as a compact unit, since it is not necessary to increase the size of the apparatus even when a focal point detection area for a high image height in vertical direction is provided along the vertical direction. However, if the image height along the horizontal direction is increased, the width of the two-dimensional image sensors also must be increased. In addition, the sensor itself constituted of a single two-dimensional image sensor is bound to become large.
A first object of the present invention is to achieve miniaturization for a focal point detection apparatus and ultimately for a camera in which a light flux having been reflected at a concave sub-mirror is guided to the focal point detection apparatus, while enabling a focal point detection over a wide range along the vertical direction.
A second object of the present invention is to miniaturize a focal point detection apparatus while achieving a focal point detection over a wide range in the photographic field along the horizontal direction.
The camera according to the present invention comprises a semi-transmissive reflecting member that reflects a light flux from a photographic optical system to an observation optical system and also allows some of the light flux to be transmitted as a light flux for focal point detection, a reflecting member constituted of a concave mirror that reflects the light flux for focal point detection having been transmitted through the semi-transmissive reflecting member and a focal point detection apparatus that detects a focal adjustment state of a subject image formed by the photographic optical system by using the reflected light flux for focal point detection. It is further provided with a correction optical system that changes the direction along which the light flux for focal point detection advances, within the optical path between the semi-transmissive reflecting member and the reflecting member. By adopting the structure described above, the first object is achieved.
The focal point detection apparatus, which is provided with a focal point detection optical system having an aperture, detects the focal adjustment state of the subject image at a predetermined image height position in the photographic field at the photographic optical system. The correction optical system changes the direction along which the light flux for focal point detection advances by deflecting, in correspondence to the image height position, the direction along which the aperture is projected backward toward the photographic optical system by the reflecting member.
The correction optical system may be formed as an integrated part of the semi transmissive reflecting member. In addition, the correction optical system and the semi-transmissive reflecting member may be formed as in the form of a plano-convex lens.
The focal point detection apparatus according to the present invention comprises an image sensor chip having a pair of two-dimensional image sensors corresponding to a focal point detection area along a substantially horizontal direction of a photographic field and a pair of two-dimensional image sensors corresponding to a focal point detection area along a substantially vertical direction of the photographic field and a focal point detection optical system that forms separate images of a light flux from a subject having passed through a photographic lens onto the pair of two-dimensional image sensors provided along the substantially horizontal direction and onto the pair of two-dimensional image sensors provided along the substantially vertical direction. In the image sensor chip, the pair of two-dimensional image sensors provided along the substantially horizontal direction over small intervals from each other along the horizontal direction are set between the pair of two-dimensional image sensors provided along the substantially vertical direction so that the pair of two-dimensional image sensors provided along the substantially horizontal direction and the pair of two-dimensional image sensors provided along the substantially vertical direction form a cross. By adopting the structure described above, the second object is achieved.
The camera according to the present invention having the semi-transmissive reflecting member, the reflecting member constituted of a concave mirror and the correction optical system that achieves the first object may employ a focal point detection apparatus that detects the focal adjustment state of a subject image formed by the photographic optical system by guiding a reflected light flux for focal point detection to the image sensor. The correction optical system may be omitted in this camera. In addition, the correction optical system may be omitted and the concave mirror may be replaced by a plane mirror in the camera.